"This was a mistake of unbelievable and unimaginable proportions," attorney Julia Yoo said on Tuesday.

Daniel Chong, 25, drank his own urine to survive and even wrote a farewell note to his mother before authorities discovered him severely dehydrated after a 2012 drug raid in San Diego.

He was held in a 5-by-10-foot cell with no windows but a peephole through the door. It had thick concrete walls and was situated in a narrow hallway with four other cells, isolated from the rest of the DEA facility, said Eugene Iredale, another of Chong's attorneys.

There was no toilet, only a metal bench on which he stood in a futile attempt to set off the sprinkler system with his cuffed hands, Chong told CNN affiliate KSWB.

He kicked the door and yelled, anything to get someone's attention, the station reported.

"I was screaming. I was completely insane," he told KWSB.

One matter still unclear is why no one heard him. Chong told the San Diego Union-Tribune last year that he heard footsteps, muffled voices and the opening and closing of cell doors, even from the cell adjacent to his. Yet no one responded to the ruckus coming from inside his cell.

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Chong was detained on the morning of April 21, 2012, when DEA agents raided a house they suspected was being used to distribute MDMA, commonly known as "ecstasy."

A multiagency narcotics task force, including state agents, detained nine people and seized about 18,000 ecstasy pills, marijuana, prescription medications, hallucinogenic mushrooms, several guns and thousands of rounds of ammunition from the house, according to the DEA.

It wasn't until the afternoon of Wednesday, April 25, that an agent opened the steel door to Chong's cell and found the handcuffed student, Iredale said last year.

Upon his release, Mr. Chong told CNN affiliate KNSD that he was visiting a friend and knew nothing about the presence of drugs and guns. He was never formally arrested or charged, the DEA said.

While detained, Chong had given up and accepted death, using a shard of glass from his glasses to carve "Sorry Mom" onto his arm as a farewell message, Yoo said. Chong lost 15 pounds and suffered from severe post-traumatic stress disorder, she said.

"He's the strongest person I have ever met," Yoo said. "As a result of his case, it's one of the primary reasons the DEA placed a nationwide policy that calls on each agent at satellite offices to check on the well-being of prisoners in their cells on a daily basis," Yoo said.

A DEA spokeswoman declined to comment extensively about the settlement and told CNN that a review of DEA procedures was conducted and submitted to the inspector general's office at the Department of Justice. She also referred CNN to a previous statement.

"I am deeply troubled by the incident that occurred here," said DEA San Diego Special Agent in Charge William R. Sherman shortly after the incident. "I extend my deepest apologies to the young man and want to express that this event is not indicative of the high standards that I hold my employees to."

Since the incident, Chong has returned to complete his undergraduate degree at UC San Diego, Yoo said. "He changed his major from engineering to economics and wants to finish school, pursue his career and help take care of his mother."